The present invention relates to a cable or belt used as a support means for elevators.
A drive pulley is often used in an elevator installation in order to move a car. In the case of such a drive pulley elevator, the drive pulley and the car are connected together by way of, for example, a cable. A drive unit sets the drive pulley into rotational movement. The rotational movement of the drive pulley is converted into linear movement of the car by a friction couple between the drive pulley and the cable. The cable then serves as a combined support and drive means, whilst the drive pulley serves as a force transmission means:                in its function as a support means the cable supports an operating weight of the elevator, consisting of the empty weight of the car, the useful load of the elevator, an optional counterweight and the weight of the cable. The cable is in that case principally loaded by tension forces. For example, the car and the counterweight are suspended from opposite ends of the cable subject to gravitational force at the support means.        in its function as a drive means for movement of the car the cable is pressed against a drive surface of the drive pulley. The cable is in that case subjected to compression and bending loads. For example, the cable is pressed by the operating weight of the elevator against a circumference of the drive pulley so that the cable and the drive pulley are disposed in friction couple.        in its function as a force transmission means the drive pulley transmits the force of the drive to the cable. Important parameters in that case are a material-specific coefficient of friction between the drive pulley and the cable and a construction-specific angle of looping of the drive pulley by the cable.        
Up to now steel cables have been used in elevator construction, which cables are connected with the drive pulley, the car and the counterweight. However, the use of steel cables is accompanied by certain disadvantages. Due to the high intrinsic weight of the steel cable, limits are placed on the travel height of an elevator installation. Moreover, the coefficient of friction between the metal drive pulley and the steel cable is so small that the coefficient of friction has to be increased by various measures such as special groove shapes or special groove linings in the drive pulley or by enlargement of the angle of looping. In addition, the steel cable acts as a sound bridge between the drive and the car which means a reduction in travel comfort. Expensive constructional measures are necessary in order to reduce these undesired effects. Moreover, steel cables tolerate, by comparison with synthetic material cables, a lesser bending cycle rate, are subject to corrosion and have to be regularly serviced.
Synthetic material cables normally consist of several load-bearing strands which are wound together and/or packed together, as can be seen from the patent documents: U.S. Pat. Nos. 4,877,422; 4,640,179; 4,624,097; 4,202,164; 4,022,010; and EP 0 252 830.
The U.S. Pat. No. 5,566,786 and the U.S. published application 2002/0000347 disclose the use of a synthetic material cable as a support or drive means for elevators, which is connected with the drive pulley, the car and the counterweight, wherein the cable consists of load-bearing synthetic material strands. The strand layer is covered, in the U.S. Pat. No. 5,566,786, by a sheath, the task of which consists of ensuring the desired coefficient of friction relative to the drive pulley and of protecting the strands against mechanical and chemical damage and ultraviolet radiation. The load is borne exclusively by the strands.
Notwithstanding the substantial advantages relative to steel cables, the synthetic material cables described in the U.S. Pat. No. 5,566,786 also demonstrate significant limitations, as also stated in the U.S. published application 2002/0000347.
Synthetic material cables demonstrate a very good longitudinal strength, which is, however, opposed by poor radial strength. The synthetic material cables tolerate, with difficulty, the load which is exerted on the outer surface thereof and which can lead to an undesired shortened service life of the cable. Finally, the modulus of elasticity of the synthetic material cables currently in use is too small for elevators with greater travel heights: undesired elongations of the cable occur and troublesome oscillations of the elevator which is set in motion are noticed by the user, particularly when the length of the cable has exceeded a specific limit.
Belts used as support or drive means are known from the U.S. published application 2002/0000347.